Induction by the Primitive Streak and its Derivatives in the Chick

Abstract

1. Specimens are described which demonstrate the induction of neural plateby (a) the mesodermal part of the primitive streak, (b) the head process and sinus rhomboidalis, and (c) neural plate. 2. The neural plate which was induced by the mesodermal part of the primitive streak was in reversed orientation as regards the host embryo. Thus the orientation of the embryo must be already fixed in the mesodermal part of the streak, and must in this case have overcome any influence which the host may be able to exert. 3. The same embryo was more complete than indicated by the presumptive fate of the tissue which induced it, whence it is concluded that the chick organiser,like the amphibian, shows a tendency to complete itself, and to this extent behaves like part of a harmonious equipotential system. 4. Grafts of the anterior part of the embryonic axis (head process and neuralplate) into the anterior part of the host blastoderm, have induced structures which in nearly all cases give indications of being heads. Inductions by posterior parts of the axis (sinus rhomboidalis) have never given such indications. 5. Grafts of the notochord have not, as yet, given satisfactory inductions.